Mechanical properties of y₂O₃-slabilized ZrO ₂ polycrystals fabricated by the solid phase mixing and sintering method

The flexural strength and fracture toughness of 2.8 mol% Y ₂O₃-stabilized zirconia polycrystals were investigated. The polycrystals were fabricated by sintering powders prepared by two different methods; the solid phase method (SPM), which involved wet dispersing and mixing using an agitator mill, and the liquid phase precipitation method (LPM). In the case of the LPM sample, the compressive residual stress on the polished surface was lower than of the SPM sample and did not depend on the grain size, while the monoclinic phase fraction on the fracture surface increased with an increase in the grain size. By contrast, for the SPM sample, the compressive residual stress depended on the grain size, and the monoclinic phase fraction on the fracture surface revealed the tendency to decrease with an increase in the grain size. The flexural strength and fracture toughness of the LPM sample were greatly influenced by the stress-induced transformation. However, mechanical properties and transformation behavior of the SPM sample in relation to grain size implied that the SPM sample was dominated not only by the stressinduced transformation but also by the compressive residual stress and the microcracks generated by the transformation. For both SPM and LPM samples, the relationship between the transformed volume Vf√h, where V_f is the tetragonal phase fraction and h is the transformed depth, and the fracture toughness was linear. The fracture toughness for the SPM sample was more strongly influenced by V_f√h than that of the LPM sample.